1. Field of the Invention
This invention relates to a combustion state-detecting system for detecting a state of combustion (misfiring) in internal combustion engines, based upon a variation in the angular velocity of the crankshaft during rotation of the engine in every combustion cycle.
2. Prior Art
To detect a cylinder of an internal combustion engine in which normal combustion does not take place due to failure in the ignition system, the fuel supply system or the like, there is conventionally known an abnormality-detecting system which detects a rate of variation in the angular velocity of the crankshaft during rotation of the engine in every combustion cycle, to thereby determine whether or not an abnormality has occurred in any of the cylinders, based upon the detected rate of variation, as proposed, for example, by Japanese Provisional Patent Publication (Kokai) No. 3-286166.
According to the above conventional system, an output from a crank angle sensor provided at the crankshaft is directly supplied to the abnormality-detecting system, and the pulse repetition period of the sensor output is measured to detect the rotational speed of the crankshaft. However, in actuality the output from the crank angle sensor always varies due to various factors, such as rotational speed vibration components due to dimensional errors (manufacturing tolerances, mounting tolerances, etc.) of the crank angle sensor, dynamic errors of the engine per se (eccentric movement, torsion, etc. of the crankshaft), or secondary rotational speed variation components due to the combustion and compression of the engine. Therefore, when such dimensional errors of the angle sensor or dynamic errors of the engine per se are large, or when the engine is in an operating condition where the rotational speed variation components are large, the abnormality determination cannot be accurately performed.
Further, according to the conventional system, in the event of occurrence of a single misfire (i.e. a misfire occurring in only one cylinder), the engine can undergo reactive vibrations due to the misfire, causing fluctuations in the angular velocity of the crankshaft. As a result, it is erroneously determined that a plurality of misfires have occurred, though actually a single misfire has occurred.
Still further, when misfires occur in a plurality of cylinders irregularly or at random, the conventional system is not capable of identifying the cylinders which actually undergo the misfires.